The present invention relates to power supply systems. More specifically, the present invention relates to a power supply mounting system for a high density printed circuit board.
All alternating current (AC) powered electronic equipment contain one or more power supplies to convert the AC input power to various lower direct current (DC) voltages needed by the circuits inside the equipment. In the prior art, a typical connection of power from the power supply to a printed circuit board on which various components such as integrated circuits (IC's) are mounted is by a wire harness. One or more printed circuit boards and peripheral devices have power coupled to them in this manner. In today's personal computers, a single large multilayer printed circuit board is usually included, a so called motherboard, and one or more IC's including the large microprocessor chip and various memory chips are mounted on this motherboard. Use of a wire harness to couple the power supply to a component on the motherboard has severe limitations as there are significant resistive losses and inductive effects in the wires of the wire harness and conductors in the multilayer printed circuit board (PCB). As is known in the art, resistive losses are determined by the amount of current squared multiplied by the resistance of the wire or conductor. Similarly, inductive effects are largely determined by the rate at which current through a wire changes and the length of the wire. Accordingly, the resistive losses and inductive effects are significant in a wire or conductor that delivers power to an IC chip or other component that has a high power demand, especially where the active component operates at a low voltage and has a wide ranging and rapidly changing current demand which can significantly affect the voltage regulation limits at the IC chip.
Unfortunately, from the perspective of worsening regulation limits due to resistive losses and inductive effects, most modern day microprocessors have an increasing power demand, lower operating voltages, and a wide ranging and rapidly changing current demand. For example, the Intel Pentium Pro microprocessor operates at 3.1 volts and has a current demand that can change from 0 to 11.2 amps in 350 nanoseconds. It is expected that future microprocessors will operate at lower voltages and significantly higher current demand. This will significantly increase resistive losses and inductive effects in wires and conductors connecting the power supply to the microprocessor. As a result of the resistive losses and the inductance of such power coupling wires or conductors, a power supply with a wire harness is not able to deliver an accurately regulated low voltage to components on the motherboard drawing large transient currents.
In addition to having resistive losses and inductive effects, wire harnesses have reliability problems in manufacturing and handling.
The above disadvantages of using wire harnesses are well known in the art and have resulted in the use of distributed power systems in some applications. In a distributed power system, a simple AC to DC power supply produces a single voltage output which is distributed around the system. Typically, the power supply produces a bus voltage of 48 volts. This voltage is preferred because it is low enough to ensure compliance with international safety standards, yet high enough to reduce distribution losses which are proportional to the square of the current. However, other bus voltages, such as 24 or 12 volts, are also possible. The distributed power system also includes one or more high density DC to DC converters (i.e., converters that have a high power output per cubic volume of space that they occupy). These high density DC to DC converters are powered by the bus voltage and are placed in close proximity to the high power demand components powered by the power source. The reduced distance between the high power demand components and the adjacent power converter significantly reduces the resistive losses and the inductive effects in the wires and conductors coupling the power converter to the component.
However, fully distributed power systems are not yet cost effective in high volume, low cost systems, such as personal computer systems. Nonetheless, some components in personal computers require a very fast response from the AC-DC or DC-DC converter to which they are coupled. For example, many high performance processor chips used in personal computers require a fast transient current response from a DC to DC converter providing a tightly regulated programmable output from 1.8 to 3.6 volts to the processor chip. The need for precise voltage regulation by such chips requires use of what is known in the art as a voltage regulator module (VRM). A VRM can be either a complete plug-in DC to DC converter or a circuit implemented on the motherboard. The addition of a VRM to a power system increases the cost of the power system by as much as 50%. Additionally, VRMs occupy valuable motherboard area. This is particularly significant when the "wasted" area under the power converter or VRM is, for example, a portion of a 12-14 layer high density high cost motherboard.
Therefore, it is desirable to tightly regulate the voltage applied to one or more IC chips mounted on a PCB. It is also desirable to reduce resistive losses and inductive effects in delivering power to components on a printed circuit board. It is also desirable to efficiently utilize the surface area of a printed circuit board.